Injectors are used more and more for delivery of medication to patients, and they are particularly useful when they are handled by the patients themselves. In order to facilitate the handling the injectors should be easy to handle with a certain degree of automatic functions, they should be reliable and obvious to the user in order to avoid erroneous use. The injectors should further be provided with safety means to prevent accidental needle sticks from used needles due to the contamination hazards.
One type of injector on the market is the so called pen injector, a rather slim fountain pen-like injector. It is either designed so that the needle is penetrated into the skin manually by the user and subsequently the user presses a button, usually on top of the injector in order to inject the medicament, or that the needle is penetrated automatically and the medicament is injected when the button is pressed.
A drawback with the latter type of injector is that the mechanism becomes rather complicated in order to obtain that degree of automation, and therefore rather costly and also that it becomes difficult to obtain a really pen-like size. On the other hand, a drawback with the first type of injector is that there might be a problem handling the injector in that the needle first has to be pushed into the body, whereby this category of patients tends to hold the injector in a sort of stabbing manner. Subsequently, for injecting the medicament, they have to change grip in order to reach and depress the activating button, which may lead to erroneous or even no injection and certainly a degree of discomfort because of bending/moving the needle during the change of grip and/or that the patient needs to use both hands in order to operate the device.
In the field of injectors there is more and more a need for the possibility of delivering a plurality of doses of medicament. Many new drugs are to be delivered in very small quantities, and these small quantities are difficult to package in one-dose containers and inject from the containers. A few solutions to this has been presented where a larger container is emptied in steps. In order to have a reasonable accuracy as regards the repetitive and accurate quantity of the delivered doses, rather complex mechanisms have been developed. In order to repeat the dose, many injectors require their power supplier to be reloaded, which requires additional handling steps that require force by the user.
A further problem associated with injecting devices capable of delivering multiple doses is how to handle the last dose. There is often a problem if a last dose remaining in the medicament container is smaller than the dose quantity required or set.